1. Field of the Invention
The present invention relates to an electromagnetic valve which is operated by an electrical signal.
2. Description of the Related Art
In the related art, a latch type electromagnetic coil which efficiently opens and closes a pathway of a fluid is known. For example, in Japanese Unexamined Patent Application Publication No. 2002-250457, a latch type electromagnetic coil is described in which a biasing member made of a coil spring or the like, which biases a plunger in a direction away from an attractor, is interposed between the plunger and the attractor.
In recent years, a reduction in power consumption has been strongly required for electrical products, and therefore, the same demand has also increased for electromagnetic valves which are operated by an electrical signal. Above all, a latch type electromagnetic valve which is energized only at the time of opening or closing and in which the state is maintained after the opening and the closing, even if energization is cut off, is very effective in terms of power consumption among electromagnetic valves, and thus demand therefor is increasing.
In this regard, in the latch type electromagnetic coil of Japanese Unexamined Patent Application Publication No. 2002-250457, valve opening is performed by attracting the plunger to the attractor by energizing a coil member so as to generate magnetic flux in the same direction as the magnetic flux of a permanent magnet, and after the valve opening, the attractive force of the permanent magnet is set so as to maintain a valve opening position due to being set to be stronger than that of the biasing member even if the energization is cut off. Further, setting is made such that the plunger is separated from the attractor by energizing the coil member so as to generate magnetic flux in the opposite direction to the magnetic flux of the permanent magnet, whereby valve closing is performed. Further, a biasing force from the biasing member in a direction in which the plunger is separated from the attractor is made larger than an attractive force from the permanent magnet, whereby a valve closing state is maintained.
However, in the latch type electromagnetic coil of Japanese Unexamined Patent Application Publication No. 2002-250457, the biasing member is disposed between the plunger and the attractor. Further, the biasing member is disposed so as to be accommodated in an external box member made of a magnetic member and having a substantially U-shaped cross-section. For this reason, since the biasing member is accommodated in the external box member, it is necessary to make the plunger very large, and as a result, the size of an electromagnetically operated coil is increased.